This project deals with the interaction of steroid hormones with the specific plasma proteins to which they bind. Studies on corticosteroid-binding globulin (CBG, Transcortin) include: affinity labeling of the binding site of both human and rat CBG; the influence of human CBG on the transport of various steroids across the perfused human placenta; the site of synthesis of rat CBG and the role of rat CBG on the disposition of corticosterone in rat hepatocyte. The hormonal influences on the plasma concentration of testosterone-estradiol-binding globulin are being examined in the rabbit.